192 II. S. WILLIAMS — THE CUBOIDES ZONE AM' [TS FAUNA. 



forms a characteristic Tully species in the local sections, it is valueless for 

 purposes of correlation (see figures L2, L3, plate 1- . 



The Productella, varietally considered, appears to be distinctive of the 

 fully, lmi it also appears to be 1< »«-;il and belongs to a race which is quite 

 sensitive to local conditions all through the Devonian and Carboniferous. 



Comparison of New York Species with European Forms. 



In the study of all these fossils, oo facte have thus far appeared which enable 

 u- to affirm other than that the fauna is the regular successor of the preced- 

 ing Hamilton fauna of the same region. Compared with species of foreign 

 I Devonian faunas, these species show less close affinities with them than with 

 their representatives in the Hamilton formation below. At the same time 

 they are nearer to the species of the middle Devonian of foreign sections 

 than to those of any other zone in those sections. Tiny indicate general 

 homotaxial relationship with the faunas of the upper part of the middle 

 Devonian of Europe. 



We are now restricted to three species: 



Orthia bulliengis, 



Strophodonta perplana var. tullierms, and 



Rhynchont lla venustula. 



Orthis tulliensis (figure 16, plate 12 is of a race not represented in the 

 Hamilton of New York. In 0. propinquaof the Corn iferous we recognize its 

 forerunner, and can trace its ancestral line well hack into the Silurian. In 

 Iowa, however, this, or a closely allied form, iowensis, is associated with a 

 Hamilton fauna; and in the European Devonian there is a representative of 

 the same race, 0. striatula, ranging with slight mutations throughout the 

 Devonian system and over the whole region of Europe and A-ia. A later 

 mutation of the same race is seen in the common Carboniferious form, Orlhis 



upinata. For the Devonian the differences recoguized between the O. 

 tullieiuria and the 0. impressa of the following Ithaca zone are no greater 

 than the differences between either one and its representatives in Europe or 

 in Iowa. 



Since the race did not appear in the I [amilton of New York, we conclude 

 that 0. tullienris came into the region by migration and not by direct 

 descent from any Hamilton form of the same region. Its appearance in the 

 following zone in New York i. e., the tthaca formation, and in the High 

 Point fauna in Ontario county — suggests thai the fauna to which it belongs 



i- more directly associated with what follows than with the N.-w York 



I [amilton buna. 



Aiiuiher point is furnished by the Btudy of this Bpecies: 0. tulliensis, in 

 respect of the variable characters of its race, presents a much greater degi 



